1. Field of the Invention
The invention relates to lithium based batteries, and particularly to the structure of lithium-sulfur batteries for providing a high energy density and increased output power.
2. Description of Related Art
Lithium-ion batteries are widely known for a plurality of applications, for example, for mobile communication, entertainment or even for high-power applications like automotive applications. In particular, for the purpose of traction in automotive applications, lithium-ion batteries involve heavy accumulative systems, for example, battery weights of 600 kg for automotive applications with a range of 400 km. Due to their electrochemical concept, lithium-ion batteries have an energy storage capacity of about 100 Wh/kg.
Therefore, it is envisaged to use lithium-sulfur batteries which promise an energy density of up to 600 Wh/kg. However, current lithium-sulfur batteries show a number of drawbacks. Firstly, discharging occurs via a reaction chain of poly-sulfides, some of which dissolve in the electrolyte. However, reaction of dissolved sulfides with an unprotected anode leads to a self-discharge and prevents re-charge of the battery to full capacity. This is also known as shuttle mechanism.
Precipitation of sulfides may occur when the dissolved sulfides are cooled or the concentration is increased. This may cause an electrical shortcut between anode and cathode.
In U.S. Pat. No. 7,029,796 B2, a lithium sulphur battery is shown in which sulphur atoms are loosely surrounded by carbon tubes. These carbon tubes are used as conductive agent. However, since the sulphur particles are provided as powder, no mechanical stable layer is provided.
Battery structures known in the prior art use a cathode which is provided by a porous carbon-sulfur composite. Cyclic deposition and decomposition of Li2S leads to the rearrangement of the microstructure. This results in the interruption of electronic contacts between carbon particles, which significantly decreases the performance of the battery.